The present invention is an improvement of the invention covered by my prior U.S. Pat. No. 4,569,073 entitled "Asymmetrical Sideband Transmission", which issued on Feb. 4, 1986.
My prior patent discloses and claims a method and apparatus for transmitting an AM carrier wave with asymmetrical sidebands. That is, where one sideband is made to intentionally have a higher amplitude level than the other sideband. The transmitted signal is unique in that when it is received by a conventional monophonic AM broadcast radio receiver having an envelope detector, it produces pleasing sound when the receiver is detuned off the carrier frequency to favor the stronger sideband. The resulting benefits and advantages are fully described in my prior U.S. Pat. No. 4,569,073.
Although my prior U.S. Pat. No. 4,569,073 discloses that asymmetrical sideband transmissions can be generated using an independent sideband (ISB) AM stereo exciter of the type covered by my prior U.S. Pat. Nos. 3,908,090 and 4,373,115, it notes that when an asymmetrical sideband transmission is received on an ISB AM stereo receiver, such as the type disclosed in my prior U.S. Pat. No. 4,018,994, the stereo image will be inherently shifted to one side by the intentional asymmetry of the sidebands, as will be clearly understood by those skilled in the art. My U.S. Pat. No. 4,569,073 notes that if only a small amount of asymmetry is used, it might be compensated for in an ISB AM stereo receiver by adjusting the "balance" control of the receiver so as to shift the reproduced stereo image back to its normal position. However, my U.S. Pat. No. 4,569,073 discloses that asymmetrical sideband transmission is otherwise primarily useful for broadcasting monophonic program material.
It is, therefore, an object of the present invention to provide an improved asymmetrical sideband AM transmission system wherein the transmitted signal will produce a pleasing pseudo-stereo effect when received by a stereo receiver of the type designed to receive symmetrical sideband, phase-separated AM stereo radio broadcasts, when such receiver is operating in its stereo mode.